Biomechanical study of normal and pathologic hands will be performed in three areas to increase basic understanding and clinical application of hand forces. The three areas to be studied involve 1) theoretical and experimental tendon and pulley force analyses, 2) theoretical and experimental analysis of joint constraint forces, and 3) validation experiments. The emphasis will involve analysis of 1) the extensor tendon mechanism and force distribution, 2) flexor tendon forces and the pulley system, and 3) kinematics and contact area of articular surfaces. Extensor tendon anatomy will be carefully studied, and force distribution will be determined with strain measurements to improve the analytic model. The study of flexor tendon pulley systems that affect tendon and joint force distribution will be performed and resultant pulley forces and pressure distribution will be determined. The effect of pulley resection and pulley reconstruction will be examined experimentally and compared with theoretical and clinical results following these procedures. The muscle length/tension relationship will be established based on in vitro and in vivo experiments. These data will be incorporated in the model so that more realistic simulation of hand function with tendon transfers and pulley resection can be performed. Ligament-capsule studies will be performed on thumb MCP and CMC joints using established techniques with application to the pathomechanics and repair of gamekeeper's thumb and thumb base arthritis. The geometry of finger and thumb MCP joint surfaces will be collected. The kinematics of MCP joint articulation will be studied analytically and the joint contact area will be studied experimentally using arhtrotomography and cross-sectional milling techniques. This information will provide the basis for the design of resurfacing arthroplasties and ligament reconstruction. Validation of the tendon force distribution will be accomplished by two experiments. First, extensor and flexor tendon forces under selected isometric functions will be directly measured by force transducer during surgery. Second, strength evaluation of patients with peripheral neuropathy and pre and post tendon transfers will be performed. This data will have direct clinical application to tendon transfers, pulley release and reconstruction, and extensor and flexor tendon repair. The overall goal of establishing analytic models, validating the results, and expanding the information to clinical applications will be continued.